1. Technical Field
This disclosure includes embodiments that may relate to a method of combustion. This disclosure includes embodiments that may relate to a system and article that uses the method.
2. Discussion of Art
An internal combustion engine may transform fuels into work or motive power through a combustion reaction. The reaction may produce byproducts such as particulate matter (PM), carbon monoxide (CO), unburned hydrocarbons (UHC), and nitrogen oxides (NOX) (e.g., nitric oxide (NO) and nitrogen dioxide (NO2)). Suitable fuels include, for example, gasoline and diesel. In combusting diesel, the diesel is injected into the engine cylinder where it is vaporized, mixed with air to form an air-fuel mixture, which is then combusted. To obtain maximum combustion of the fuel with the oxygen in the air, it is desirable to provide a uniform air-fuel mixture in the cylinder. However, this is not always possible on a local scale within the cylinder. When the air-fuel mixture is not uniformly mixed, especially when there is a higher local ratio of fuel to air, the fuel does not undergo combustion with oxygen and forms particulate matter in the form of soot.
In addition, when the air-fuel mixture is available in the right ratio, the fuel may burn uniformly to form nitrogen oxides. When the fuel combusts in the presence of oxygen and nitrogen, the temperatures may increase to about 2,500 Kelvin to about 3,000 Kelvin. The formation of nitrogen oxides is exponentially temperature dependent. The slope of this rate increases drastically above 2,000 Kelvin. In other words, as the temperature of combustion increases above 2,000 Kelvin, significantly larger amounts of nitrogen oxides are produced. It may be desirable to minimize nitrogen oxides and particulate matter emissions into the environment.
One method of removing nitrogen oxides from an exhaust fluid involves a post combustion selective catalytic reduction (SCR) process in which nitrogen oxides are reduced. For example, an ammonia-SCR process may use ammonia as a reducing agent in the selective catalytic reduction process to produce nitrogen gas and water. Ammonia-SCR, also referred to as NH3-SCR, may be used because of its catalytic reactivity and selectivity. However, practical use of ammonia has been largely limited to power plants and other stationary applications.
The selective catalytic reduction of nitrogen oxides with hydrocarbons (HC-SCR) may compete with the NH3-SCR process. The hydrocarbon reductant reacts with the nitrogen oxides in the exhaust stream to form primarily nitrogen gas and carbon dioxide. The selective catalytic reduction process uses hydrocarbons as the reducing species as opposed to ammonia. Both the approaches require catalysts. However, these catalysts may present a narrow operating temperature range and deactivate relatively quickly in the presence of SO2.
Accordingly, it may be desirable to have a system and method that differs from those systems and methods currently available.